SURFACE MOUNT PROCESS

Reflow soldering ndiyo inonyanya kushandiswa nzira yekubatanidza pamusoro pegomo zvinhu kune akadhindwa edunhu mabhodhi (PCBs).Chinangwa chemaitiro acho ndechekugadzira majoini anogamuchirika ekutengesa nekutanga pre-kupisa zvikamu / PCB / solder paste uyezve kunyungudutsa solder pasina kukuvadza nekupisa.

Izvo zvakakosha zvinotungamira kune inoshanda reflow soldering maitiro ndeaya anotevera:

1. Inokodzera muchina
2. Inogamuchirwa reflow profile
3. PCB/chikamu footprint Dhizaini
4. Kunyatsodhindwa PCB uchishandisa stencil yakagadzirwa zvakanaka
5. Kudzokororwa kuiswa kwepamusoro-soro zvikamu
6. Yakanaka mhando PCB, zvikamu uye solder paste

Inokodzera Machine

Kune mhando dzakasiyana dze reflow soldering muchina unowanikwa zvichienderana neinodiwa mutsara kumhanya uye dhizaini / zvinhu zvePCB maassemblies kuti agadziriswe.Ovheni yakasarudzwa inoda kuve yehukuru hwakakodzera kubata mwero wekugadzira wepiki uye nzvimbo yemidziyo.

Kumhanya kwemutsara kunogona kuverengerwa sezvinoratidzwa pazasi: -

Kumhanya kwemutsara (zvishoma) =Mabhodhi paminiti x Kureba pabhodhi
Load Factor (nzvimbo pakati pemapuranga)

Izvo zvakakosha kuti titarise kudzokorora kwemaitiro uye saka iyo 'Load Factor' inowanzotsanangurwa nemugadziri wemuchina, kuverenga kunoratidzwa pazasi:

Kuti ukwanise kusarudza saizi chaiyo reflow ovheni kukurumidza kwekuita (kunotsanangurwa pazasi) kunofanirwa kunge kwakakura kudarika kudiki kwakaverengerwa mutsara kumhanya.

Process speed =Ovheni kamuri kudziyisa kureba
Process yekugara nguva

Pazasi pane muenzaniso wekuverenga kumisa saizi chaiyo yeovheni: -

SMT assembler inoda kugadzira 8-inch board pamwero we180 paawa.Iyo solder paste mugadziri anokurudzira 4 maminetsi, matatu nhanho mbiri.Inguva yakadii hovhoni yandinofanira kugadzira mabhodhi pakubuda uku?

Mabhodhi paminiti = 3 (180/awa)
Kureba pabhodhi = 8 inches
Load Factor = 0.8 (2-inch nzvimbo pakati pemapuranga)
Process Kugara Nguva = 4 maminitsi

Verenga kumhanya kwemutsara:(3 mapuranga/miniti) x (8 inches/bhodhi)
0.8

Kumhanya kwemutsara = 30 inches/miniti

Naizvozvo, ovheni yereflow inofanira kunge iine kukurumidza kukurumidza kweinenge 30 inches paminiti.

Sarudza hurefu hwekamuri yekudziya ne process speed equation:

30 mu/min =Ovheni kamuri kudziyisa kureba
4 maminitsi

Hurefu hwakapisa huni = 120 inches (10 tsoka)

Ziva kuti hurefu hwehovhoni huchapfuura 10 tsoka kusanganisira yekutonhora chikamu uye conveyor kurodha zvikamu.Iko kuverenga ndeyeKUPISWA KUREREVA - KWETE KWEOVEN LENGTH.

2. Yakavharwa loop control yekumhanyisa mafeni econvection - Kune mamwe mapeji epamusoro epamusoro seSOD323 (ona kuisa) ayo ane nzvimbo diki yekusangana kusvika kuhuwandu hwehuwandu iyo inogona kukanganiswa panguva yekuyerera.Yakavharwa loop yekumhanyisa kudzora yevatevedzeri vegungano isarudzo inokurudzirwa kumagungano anoshandisa zvikamu zvakadaro.

3. Automatic control of conveyor and center-board-support widths - Mimwe michina ine manual hupamhi gadziriso asi kana paine akawanda akasiyana maassembly kuti agadziriswe nekusiyana PCB hupamhi saka iyi sarudzo inokurudzirwa kuchengetedza maitiro anoenderana.

Inogamuchirwa Reflow Profile

Kuti ugadzire reflow profile thermocouples akabatana nesample assembly (kazhinji ine tembiricha solder) munzvimbo dzinoverengeka kuyera huwandu hwetembiricha mhiri kwePCB.Zvinokurudzirwa kuve neinenge imwe thermocouple iri padhi yakananga kumucheto kwePCB uye imwe thermocouple iri pane padhi yakananga pakati pePCB.Zvakanakira mamwe thermocouples anofanirwa kushandiswa kuyera huwandu hwakazara hwetembiricha mhiri kwePCB - inozivikanwa se'Delta T'.

Mukati meyakajairwa reflow solder profile pane kazhinji matanho mana - Preheat, soak, reflow uye kutonhora.Chinangwa chikuru chiri chekuendesa kupisa kwakakwana mugungano kuti rinyungudutse solder uye kugadzira majoini ekutengesa pasina kukuvadza kune zvikamu kana PCB.

Preheat- Munguva iyi zvikamu, PCB uye solder zvese zvinopiswa kune yakatarwa soak kana kugara tembiricha uchichenjerera kuti usakurumidza kupisa (kazhinji haipfuuri 2ºC/sekondi - tarisa solder paste datasheet).Kupisa nekukasira kunogona kukonzera kuremara kwakadai sezvikamu kutsemuka uye solder paste kuti splatter ichikonzera solder mabhora panguva yekuyerera.

Soak- Chinangwa chechikamu ichi ndechekuona kuti zvikamu zvese zviri kusvika kune tembiricha inodiwa usati wapinda padanho rekuyerera.Soak inowanzotora pakati pemasekonzi 60 ne120 zvichienderana ne 'kusiyana kukuru' kwegungano uye mhando dzezvikamu zviripo.Kunyanya kushanda kwekupisa kwekushisa panguva yekunyorova nguva shoma inodiwa.

Kana iyo reflow profile isina kukwana kupisa kwakaiswa panguva yereflow nhanho pachave neanotengeswa majoini anoonekwa akafanana nemifananidzo iri pazasi: -

solder isina kuumbwa fillet ine lead

Haasi ese mabhora ekutengesa akanyunguduka

A common soldering defect mushure me reflow ndiko kuumbwa kwe mid-chip solder balls/beads sezvinoonekwa pazasi.Mhinduro yekukanganisika uku ndeyekugadzirisa stencil dhizaini -mamwe mashoko anogona kuonekwa pano.

Kushandiswa kwenitrogen panguva yekudzokazve kunofanirwa kutariswa nekuda kwemaitiro ekufamba kubva kune solder paste ine yakasimba fluxes.Iyo nyaya haisi iyo yekugona kuyerera zvakare munitrogen, asi kugona kuyerera zvakare mukushaikwa kweokisijeni.Kupisa solder pamberi peokisijeni kunogadzira maokisi, ayo anowanzo asiri ekutengesa.

Kutonhodza- Iyi ingori nhanho panguva iyo gungano rinotonhodzwa asi zvakakosha kuti usatonhodze gungano nekukurumidza - kazhinji mwero unokurudzirwa wekutonhora haufanire kudarika 3ºC/sekondi.

PCB/Component Footprint Dhizaini

Pane akati wandei maficha ePCB dhizaini ane pesvedzero yekuti gungano richayerera sei.Muenzaniso uri saizi yemanjanji akabatana nechikamu chetsoka - kana track inobatanidza kune rimwe divi rechikamu chetsoka yakakura pane imwe izvi zvinogona kutungamira mukusaenzana kwemafuta zvichiita kuti chikamu chive 'guva' sezvinoonekwa pazasi:-

Mumwe muenzaniso ndewe 'copper balancing' - magadzirirwo mazhinji ePCB anoshandisa nzvimbo hombe dzemhangura uye kana pcb ikaiswa mupaneru kubatsira magadzirirwo ekugadzira inogona kutungamira mukusaenzana kwemhangura.Izvi zvinogona kuita kuti pani iite kutenderera panguva yekuyerera uye saka mhinduro inokurudzirwa ndeyekuwedzera 'copper balancing' kunzvimbo dzemarara dzepaneru sezvinoonekwa pazasi:-

Maona'Design for Manufacture'kune dzimwe pfungwa.

Kunyatsodhindwa PCB uchishandisa stencil yakagadzirwa zvakanaka

Iwo ekutanga maitiro matanho mukati mepamusoro pegomo musangano akakosha kune inoshanda reflow soldering process.Thesolder paste kudhinda maitirochinhu chakakosha kuti ive nechokwadi chekuisa dhipoziti ye solder paste paPCB.Chero kukanganisa panguva ino kunotungamira kune zvisingadiwe mhedzisiro uye saka kutonga kwakazara kweiyi maitiro pamwe cheteinoshanda stencil designzvinodiwa.

Kudzokororwa kuiswa kwepamusoro pegomo components

Musiyano wekuiswa kwechikamu

Kuiswa kwepamusoro pegomo zvinhu kunofanirwa kudzokororwa uye saka yakavimbika, yakanyatsochengetedzwa yekutora uye kuisa muchina unodiwa.Kana zvikamu zvepakeji zvisina kudzidziswa nenzira kwayo zvinogona kukonzera kuti michina yekuona sisitimu isaone chikamu chimwe nechimwe nenzira imwechete uye saka musiyano mukuiswa uchaonekwa.Izvi zvinotungamira kune zvisingaenderane mhedzisiro mushure mekuyerera kwe soldering process.

Zvirongwa zvekuisa zvikamu zvinogona kugadzirwa uchishandisa pick nekuisa michina asi maitiro aya haana kururama sekutora ruzivo rwecentroid kubva kuPCB Gerber data.Kazhinji iyi data yecentroid inotumirwa kunze kubva kuPCB dhizaini software asi imwe nguva haisi kuwanikwa uye saka iyosevhisi yekugadzira iyo centroid faira kubva kuGerber data inopihwa neSurface Mount process.

Michina yese yekuisa michina ichave ne 'Placement Accuracy' inotsanangurwa senge:-

35um (QFPs) kusvika 60um (chips) @ 3 sigma

Izvo zvakakoshawo kuti muromo wakakodzera usarudzwe kuti rudzi rwechikamu chiiswe - huwandu hweakasiyana echikamu chekuisa nozzles anogona kuonekwa pazasi:-

Yakanaka mhando PCB, zvikamu uye solder paste

Hunhu hwezvinhu zvese zvinoshandiswa panguva yekuita hunofanirwa kunge hwakakwirira nekuti chero chinhu chehurombo chinotungamira kune zvisingadiwe mhedzisiro.Zvichienderana nekugadzirwa kwePCB's uye nzira yavakachengeterwa kupera kwePCB's kunogona kutungamirira kune hurombo solderabilty panguva yereflow soldering process.Pazasi pane muenzaniso wezvinogona kuoneka kana kupedzwa kwepamusoro paPCB kwakashata zvichitungamira kune chirema chinozivikanwa se'Black Pad': -

YAKANAKA QUALITY PCB PEDA

TARNISHED PCB

Solder inoyerera kune chikamu uye kwete PCB

Nenzira imwecheteyo kunaka kwechikamu chepamusoro chechikamu chinotungamira chinogona kuve chakashata zvichienderana nekugadzira nzira uye nzira yekuchengetedza.

Unhu hweiyo solder paste inobatwa zvakanyanya neiyokuchengetedza uye kubata.Yakashata mhando solder paste kana ikashandiswa inogona kupa mhedzisiro sezvinoonekwa pazasi: -